The explosive growth of mobile telecommunication networks demands flexible, efficient, high performance receivers, for example, base stations in cellular networks. In a wireless CDMA communication network, multiple access interference (MAI) is one of the major factors that limits the performance of the network. To combat the effect of MAI, many digital receivers have been proposed. However, prior art digital receivers are generally characterized by a fairly high computational complexity.
The major cause of the computational complexity lies on the block-based processing in the receivers, i.e., the receivers detect the signal based on a block of received samples. Multi-user receivers also require a great deal of additional information which typically includes a code sequence, relative timing, carrier phase, and sometimes the instantaneous received signal strength for each mobile transmitter or transceiver, e.g., a cellular telephone.
Channel fading is another cause of performance degradation in wireless communication networks. The increased mobility of receivers in wireless communication networks often results in fast fading and the resulting Doppler spread substantially degrades the receiver performance.
Recently, minimum mean square error (MMSE) receivers have been developed. As an advantage, a MMSE receiver has a lower complexity and the detection decision is made on a per symbol basis. In addition, a MMSE receiver with space diversity features has been described for multi-user detection, see Cho et al., “Adaptive Interference Cancellation with Diversity Combining for a DS-CDMA System in Rayleigh Fading,” Proc. of IEEE VTC'99, May 1999. Due to the use of diversity combining technique, network performance and capacity are is improved.
However, in the case of a fast fading channel, little performance improvement can be achieved, even if the diversity dimension is increased. One way to combat fast fading channels in CDMA networks is to use of time-frequency diversity combining techniques, see U.S. patent application Ser. No. 09/487,095 “Software-Based Digital Receiver Adaptable to Multiple Multiplexing Schemes,” filed by Horng at al. on Jan. 19, 2000. However, that receiver can only detect a single user. With the increased mobility of receivers, frequency diversity becomes more and more important because high mobility introduce severe frequency drifts on the transmitted signals.
Therefore, it is desired to provide a multi-user receiver that has a greater capacity, a lower bit rate error, and that is less susceptible to channel fading and multiple-access interference.